Monocular Buying Guide

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Monocular Buying Guide

Monoculars are a mixed combination of a telescopes and a pair of binoculars. Like binoculars, they use lenses and prisms to reflect light in order to magnify an image, but like telescopes they contain just a single body and viewing lens. While magnification levels are often no match for top-of-the-range telescopes, a monocular can be a suitable alternative to standard binoculars and may even carry some advantages over the more popular viewing device.

Monocular Vs. Binocular

Both monoculars and binoculars are excellent devices for magnifying objects and images and are commonly used outside in nature to get close up views of far off mountains or birds in a tree, for example. However, there are differences between the two pieces of equipment that mean some people prefer binoculars and some monoculars.

Magnification levels of both devices are similar, typically ranging from 4x zoom to over 25x, so technically they are very alike. So perhaps the greatest advantage comes in terms of weight and size, both of which are generally less than half that of a standard pair of binoculars, making them much more portable and ideal for walkers and hikers to pack into their rucksacks. In terms of image quality, monoculars are far less susceptible to slight movement, unlike binoculars which do suffer from unsteadiness, and due to the single body, the common binocular complaint of non-aligned lenses is moot. Despite these advantages, it is important to remember that monoculars do not offer the same depth as binoculars, as viewing through a single eye reduces viewing depth significantly.

Choosing a Monocular

When choosing a monocular, it is important to consider a range of factors to ensure purchasing the best possible device for the intended purpose. Be sure to take into account the level of magnification, the lens coating, and the optical design of the monocular before committing to a specific make or model.

Monocular Magnification

The magnification of a monocular is how much larger the equipment makes the viewed image. There are advantages to both lower and larger levels of magnification depending on the intended use of the monocular. Specifications will usually include two numbers, 4x28 for example, where the 4x refers to the magnification.

4x - 8x

Monoculars with very low magnification mean the image zoom is small, but the field of vision is very large. These monoculars are good for viewing an entire landscape rather than a single object. They are also suitable for children.

8x - 9x

A slightly higher magnification although this is still considered quite low. Field of vision remains large, and the image benefits from greater brightness and clarity. Again, these monoculars are suitable for wide landscapes and for children.

10x - 14x

As the magnification level becomes higher, the field of vision diminishes although these mid-range monoculars offer a good compromise between the two aspects. They are a good, all-round choice, particularly for novices.

15x - 19x

Although monoculars are quite protected from the effects of shaking, they are not immune, so a steady hand is needed for this higher magnification to ensure a clear image.

20x - 25x

The field of view on these high magnification monoculars is low, but magnification is excellent. These monoculars are particularly suited to viewing a specific object, such as an animal in the distance or a small bird in a large tree for example.

Monocular Lens Coating

Monoculars are available with varying coating on the lenses, ranging from simply coated to the more sought after, and costly, fully multi-coated. The type of coating affects the brightness of the viewed image, with the more expensive coatings reducing glare to increase brightness and clarity.

Fully Multi-Coated

This coating is the most costly but most beneficial in terms of image brightness. A combination of anti-reflective coatings are used, and these monoculars also tend to include a waterproof coating to increase durability and longevity.


Despite using cheaper, more reflective materials for the coating, monoculars that are multi-coated are still considered excellent quality. The resolution is much higher than devices that are simply coated, and they are a good alternative to fully multi-coated.

Fully Coated

Fully coated monoculars use just a single material to coat the lens, meaning they are more susceptible to sunlight and glare which can reduce the quality of the image and cause blurriness at the edges. However, these monoculars are more affordable and good for novices.


Lenses that are simply described as coated are often budget models that lack the same quality as the others. Of course, they still do the job but should only be used in non-direct light for optimal results.

Monocular Optical Design

Monocular lenses, particularly those widely available on the UK market, use either roof or porro prisms, containing smaller prisms within to magnify the image, while others use the 17th century Galilean technique. The type of prism really depends upon the magnification level of the monocular.

Roof Prism

A roof prism is constructed like a roof, with two faces that come together at 90 degrees. Roof prisms are commonly found within higher magnification models as they work best with a greater focal distance.

Porro Prism

Porro prisms are the most popular optical design of monoculars. They are quite similar, and often mistaken for, roof prisms, but produce a directly erect image, rather than an inverted image that needs further technology to correct the orientation.


The Galilean design also produces an erect image, but the field of vision is very small. This means that this design is not suited to higher magnification models as the field of vision would become too small, so the design is mostly seen on lower magnification monoculars.

Lens Diameter Considerations

In monocular specifications, there will usually be two numbers, such as 4x28. As discussed, the 4x refers to the magnification level. However, the 28, or the number that comes after the x, refers to the lens diameter and is an important consideration when choosing a monocular. The required lens diameter will largely depend on the intended use of the monocular. As a general rule, the larger the diameter, the more light that can be let into the equipment. This means that monoculars with a large lens diameter are particularly suited to being used in poor lighting conditions, while a smaller lens will suffice if the monocular is primarily for sunny, daytime use. If planning to use in very dark conditions, consider a lens that is more than 35mm in diameter. However, be sure to keep in mind that the larger the lens, the heavier, larger, and bulkier the monocular, so these models may not be as portable as more compact versions.


A monocular is a suitable alternative to a standard pair of binoculars and is a good compromise between binoculars and a telescope. It gives the same excellent magnification range as a pair of binoculars but, with just a single lens and body, is typically much more portable and compact, particularly if containing a small lens diameter.

There are a number of factors to take into account when choosing a monocular. High magnification levels bring the image closer, yet lower magnification levels allow for a greater field of vision, perfect for viewing landscapes. Fully multi-coated lenses produce the clearest image, but are typically the most costly options, so buyers should consider browsing websites such as eBay to find the best prices. Also consider the lens diameter. Remember, if planning to use the monocular in a similar fashion to a telescope, primarily for stargazing at night, it is best to choose a monocular with a very large lens to let enough light in, preferably one over 35mm.

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